Up to now, various array antenna apparatuses have been proposed as variable directivity antenna apparatuses for use in a wireless communication system employing, for example, the MIMO wireless method (See Patent Documents 1 and 2, for example).
The Patent Document 1 discloses an array antenna apparatus, which has a structure simpler than that of an antenna according to prior art and can easily form an excitation element and parasitic elements. The array antenna apparatus is characterized as follows. At least one dielectric substrate on which at least one of a plurality of parasitic elements is provided around an excitation element. Alternatively, the array antenna apparatus includes the excitation element and a first dielectric substrate on which at least one of the plurality of parasitic elements is formed, and at least one second dielectric substrate is provided around the excitation element, where at least one further parasitic element among the plurality of parasitic element is formed on the second dielectric substrate.
In addition, the Patent Document 2 proposes an antenna apparatus which can control directivity or omni-directivity, radiation polarization, and a radiation direction of the antenna apparatus to provide a desired state without increasing size and cost of the antenna apparatus, by devising a structure of each antenna element. The antenna apparatus includes a conductive excitation element, parasitic elements each made of semiconductive plastics, and control electrodes connected to these parasitic elements, respectively, where the conductive excitation element and the parasitic elements have predetermined lengths and arranged on a dielectric substrate, respectively. Direct-current bias voltages supplied to the control electrodes are controlled to change over the parasitic elements to have insulating properties or conductive properties. The antenna apparatus is characterized as follows. Two parasitic elements changed over to have the conductive properties are combined to configure a directional antenna apparatus including a wave director, a reflector and the like. In addition, the wave director and the reflector other than this excitation element (feeder) are made to have the insulating properties to configure an omni-directional antenna apparatus.